Advice needed on new rehomed cat please

If he wees/poos on the floor again, pour some cat litter onto it and then dump the wet cat litter into the litter box. Sounds grim but cats are very fastidious and like to go in the same place every time - so if there is a litter tray that smells clearly of wee he will be much more likely to go in there as that smells like 'toilet'.

We brought home a lovely boy aged approximately 3 yesterday. Obviously a bit shy but beautiful cat. Trouble is after using the litter tray once, he has done a wee and a poo in the same spot on my kitchen floor. We have shown him the litter box and I think at nights I will take the lid off but this is not practical with a 3 year old who gets into everything. Any advice on how to encourage use? I have been taking him to the tray every few hours. Is it usual for outdoor cats to hold it in until they actually go out? I know he is getting use to his surroundings but am at a loss. Thanks